1. Field of the Invention
The present invention relates to a protective film removing device for removing a water-repellent protective film formed on a surface of a substrate by dissolving the water-repellent protective film in a liquid remover and recovering a mixed chemical solution, which is a mixture of the liquid remover and a solution produced by dissolving the water-repellent protective film in the liquid remover, and a method of recovering the mixed chemical solution.
2. Description of the Related Art
A photolithographic technique for a semiconductor device fabricating process includes, for example, the steps of forming a resist film on a semiconductor wafer (hereinafter, referred to simply as “wafer”) exposing the resist film to light through a photomask, and developing the exposed resist film by a developing process to form a desired resist pattern.
An exposure technique disclosed in JP-A 2005-175079 forms a liquid layer that transmits light on a surface of a wafer and exposes the wafer through the liquid layer. Hereinafter, this exposure technique will be referred to as an immersion exposure method. The immersion exposure method uses a characteristic nature of light that the wavelength of light reduces when light travels in a liquid layer, such as a pure water layer. For example, the wavelength of 193 nm of light emitted by an ArF light source decreases to 134 nm in water. Thus a high-resolution exposure process can be achieved by using an existing argon fluoride light source (ArF light source) or an existing krypton fluoride light source (KrF light sources).
Studies have been made to suppress the elution of the resist during immersion exposure and to make a liquid layer used for immersion exposure on a surface of a wafer difficult to remain on the surface of the wafer by forming a water-repellent protective film on the surface of the wafer after coating the surface with a liquid resist. A technique mentioned in JP-A 2005-183709 removes a water-repellent protective film formed on a surface of a wafer with a chemical solution (remover) in a developing system, and recovers the used chemical solution. A diluted developer or a thinner is used as the chemical solution to remove a protective film soluble in an alkaline solution. A fluorocarbon solvent or the like us used as the chemical solution to remove a protective film insoluble in an alkaline solution.
Abilities and costs of protective films will be examined. The latter protective film insoluble in an alkaline solution is superior in ability to the former protective film soluble in an alkaline solution. However, the latter protective film is more costly than the former protective film. The protective film insoluble in an alkaline solution is a film of a fluorocarbon resin. A fluorocarbon solvent is used as remover for removing the protective film of a fluorocarbon resin. The protective film of a fluorocarbon resin and the fluorocarbon solvent are costly. The inventors of the present invention made studies to recover a mixed chemical solution containing the remover and the solution produced by dissolving the protective film in the remover to recycle those chemicals. Since those chemicals are highly volatile, the recovery percentage of those chemicals is very small. The recovery percentage is between several percent and about 50% for a 300 mm diameter wafer.
A method of preventing the natural gasification (volatilization) of a highly volatile cleaning solvent, such as PFC (perfluorocarbon), HCFC, HFC or the like, mentioned in JP-A 2005-175079 forms an oil film over the surface of a cleaning solvent contained in a cleaning tank by discharging an oil having a specific gravity smaller than that of the cleaning solvent by an oil discharging device toward the surface of the cleaning solvent contained in the cleaning tank to form an oil film over the surface of the cleaning solvent to prevent the volatilization of the cleaning solvent. However, nothing about a method of solving the foregoing problem is mentioned in JP-A 2005-175079.